Due to the inability of conventional elastomeric components to function well in high temperature or corrosive environments encountered in oil and gas wells, there exists a need for a seal for use in downhole well equipment that will withstand harsh environmental conditions. Such a seal is needed on various well tools such as packers, expansion joints and subs. For example, packers are used in steam injection wells to provide a zone isolating pressure sealing tool that establishes an annular seal between the well casing and the well tubing. In this particular type of application, the steam injection well's operating characteristics create a severe test which conventional sealing materials are unable to meet. In the steam injection process, the injection phase of the operation causes the well equipment to approach temperatures of 650.degree. F., but during the producing phase, the temperatures drop to as low as 80.degree. F. This substantial temperature range, when coupled with pressure differential reversals that commonly occur in downhole environments, subject the well tool seals to conditions which they are unable to overcome. Although semi-elastomers and fiber-type materials such as asbestos and other types of materials such as disclosed in U.S. Pat. No. 4,444,403 have been suggested to combat this problem, their success has been limited.
One feature of the present invention is to provide an expandable metal seal for a well tool and one that will seal in spite of rough surface conditions on the well casing.
Another feature of the present invention is the provision of a series of expansion rings positioned in the seal-setting mechanism for increasing the setting force applied to the seal when the temperature increases. The expansion rings may be a pair of bimetallic expansion rings in which the coefficient of thermal expansion of one of the pair is much greater than the other or the pair of rings may be shape memory effect springs.